An Evolved Packet System (EPS) of the 3rd Generation Partnership Project (3GPP) is composed of an Evolved Universal Terrestrial Radio Access Network (E-UTRAN), a Mobility Management Entity (MME), a Serving Gateway (S-GW), a Packet Data Network Gateway (P-GW), a Home Subscriber Server (HSS), a 3GPP Authentication Authorization Account (AAA) server, a Policy and Charging Rules Function (PCRF) and other supporting nodes.
FIG. 1 is a schematic diagram of a system structure of EPS in the related art, wherein, the MME is responsible for the related work of a control plane, such as a mobility management, a processing of non access stratum signalings, a management of the user mobile management context and so on; the S-GW is an access gateway device connecting with the E-UTRAN, is used to forward data between the E-UTRAN and the P-GW, and is responsible for buffering the paging waiting data; and the P-GW is a border gateway between the EPS and the Packet Data Network (PDN) network, and is responsible for functions such as the access of the PDN, forwarding data between the EPS and the PDN and so on;
the EPS supports the intercommunication with a non 3GPP network, and implements the intercommunication with the non 3GPP network through S2a/b/c interfaces. The non 3GPP network includes the trusted non 3GPP network and the un-trusted non 3GPP network. The IP access of the trusted non 3GPP network can interface with the P-GW directly through the S2a interface; and the IP access of the un-trusted non 3GPP network is required to connect with the P-GW through an Evolved Packet Data Gateway (ePDG), and the interface between the ePDG and the P-GW is the S2b.
If the EPS supports a Policy and Charging Control (PCC), then the PCRF makes the a policy and charging rule; the PCRF connects with the IP service network of an operator through a receiving interface Rx, and obtains the service information; besides, the PCRF connects with the gateway devices in the network through Gx/Gxa/Gxc interfaces, and is responsible for initiating the establishment of IP bearer, ensuring the Quality of Service (QoS) of the service data, and performing the charging control, wherein a Policy and Charging Enforcement Function (PCEF) is located in the P-GW, the PCRF and the P-GW exchange information through the Gx interface. When the interface between the P-GW and the S-GW is based on the Proxy Mobile IP (PMIP), a Bearer Binding and Event Report Function (BBERF) exists in the S-GW, and the S-GW and the PCRF exchange information through the Gxc interface. When accessing through the trusted non 3GPP network, there is also a BBERF residing in the trusted non 3GPP access gateway, and the access gateway of the trusted non 3GPP network and the PCRF exchange information through the Gxa interface. When the User Equipment (UE) is roaming, the interface between the home PCRF and the visited PCRF is an S9 interface, and at the same time, the Application Function (AF) providing services for the UE is located in the service network, and sends service information for generating the PCC policy to the PCRF through the Rx interface.
In the related art, the protocol used in the PCC architecture is a Diameter application protocol developed based on a Diameter Base Protocol, such as the application protocol applied in the Gx interface, the application protocol applied in the Rx interface, the application protocol applied in the Gxx interface (including the Gxa and the Gxc interfaces), the application protocol applied in the roaming interface S9 and so on. These application protocols define messages, commands, Attribute Value Pairs (AVP) and so on for the PCC. The Diameter sessions established by these protocols can be respectively called as a Gx session, a Gxx session, an Rx session and an S9 session. Various function entities of the PCC, through these sessions, perform the policy and charging control on the PDN connection established for the UE accessing network.
The EPS system supports the Multiple PDN access (multi-PDN accessing), that is, the UE can access multiple PDNs simultaneously through multiple P-GWs or one P-GW, and the EPS supports that the UE accesses simultaneously the same PDN many times. In the 3GPP, the corresponding PDN network can be found through the Access Point Name (APN, which also can be called as the PND identifier). Therefore, it can be considered that the UE can simultaneously access the same APN many times. Generally, one connection from the UE to the PDN network is called as one IP Connectivity Access Network (IP-CAN) session, and thus the EPS supports that the UE can have multiple IP-CAN sessions to one PDN at the same time.
FIG. 2 is a flow chart of the UE accessing the same APN twice (namely, establishing two PDN connections/IP-CAN sessions to the same PDN) through the trusted non 3GPP access network in the non roaming scenario according to the related art, and the specific steps are as follows:
step S201, the UE accesses the trusted non 3GPP access network by enforcing a specific processing procedure of the non 3GPP with the trusted non 3GPP access network;
step S202, the UE makes a request for performing a EPS access authentication to the HSS/AAA through the trusted non 3GPP access network after accessing the trusted non 3GPP access network; the HSS/AAA authenticates the UE which sends the request after receiving the EPS access authentication request; and the HSS/AAA sends P-GW selection information subscribed by the user and the APN subscribed by the user, including a default APN, to the trusted non 3GPP access gateway after completing the authentication on the UE, and below the “APN” denotes the “default APN” in the case that there is no ambiguity;
step S203, a layer 3 attachment flow is triggered after the authentication succeeding;
step S204, the trusted non 3GPP access gateway supports to establish multiple PDN connections to a single APN, and the trusted non 3GPP access gateway allocates a packet data network connection identifier1 (PDN Connection Id1) for uniquely differentiating the PDN connection to be established;
the BBERF residing in the trusted non 3GPP access gateway sends an indication message of gateway control session establishment to the PCRF, and a user identifier Network Access Identifier (NAI), a PDN identifier APN and the PDN Connection Id1 are carried in that message; that message makes a request for establishing one gateway control session (i.e., the Gxx session), which is identified as Gxx session1.
Step S205, the PCRF makes the PCC rule and QoS rule according to user subscription information, a network policy, an access network bearer attribute and so on, and at the same time, the PCRF may also make a corresponding event trigger; the PCRF sends the QoS rule and the event trigger to the trusted non 3GPP access gateway through a gateway control session establishment acknowledge message; and the trusted non 3GPP access gateway installs the QoS rule and the event trigger, and these rules are not policies regarding to the specific services, but are some default policies;
step S206, the trusted non 3GPP access gateway selects the P-GW according to the received P-GW selection information, and sends a proxy binding update message to the selected P-GW, wherein the user identifier NAI, the PDN identifier APN and the PDN Connection Id1 are carried in that message;
step S207, the P-GW allocates an IP address, which is identified as IP Address1, of the established PDN connection for the UE;
the PCEF residing in the P-GW sends an indication message of IP-CAN session establishment to the PCRF, and the user identifier NAI, the IP Address1, the PDN identifier APN and the PDN Connection Id1 are carried in that message; that message makes a request for establishing one Gx session, which is identified as the Gx session1.
Step S208, the PCRF associates the indication message of IP-CAN session establishment with the previous the indication message of gateway control session establishment according to the user identifier NAI, the PDN identifier APN and the PDN Connection Id1 after receiving the indication message of IP-CAN session establishment, that is, associates the gateway control session (Gxx session1) established in step S204 with the IP-CAN session (Gx session1) established in step S207; at the same time, the PCRF inquires the user subscription information, updates the previously made rules (including the PCC rule, the QoS rule and the event trigger) according to the user subscription information, the network policy, the access network bearer attribute and so on, and the PCRF sends an IP-CAN session establishment acknowledge message to the PCEF in the P-GW, wherein the PCC rule is carried in that message; and the above rules are not the policies regarding to the specific services, but are some default policies;
step S209, the PCEF which is located in the P-GW installs and enforces the PCC rule carried in the IP-CAN session establishment acknowledge message after receiving the IP-CAN session establishment acknowledge message, and at the same time, the P-GW sends its own IP address to the HSS;
step S210, the P-GW returns a proxy binding acknowledge message to the trusted non 3GPP access gateway, and the proxy binding acknowledge message includes the IP address (IP Address1) allocated by the P-GW for the PDN connection established by the UE;
step S211, if the QoS rule made in step S208 is different from that sent down in step S205, then the PCRF sends the updated QoS rule down to the BBERF in the trusted non 3GPP access gateway through the gateway control and QoS policy rule provision message;
step S212, the BBERF in the trusted non 3GPP access gateway installs the QoS rule, and returns the gateway control and QoS policy rule provision acknowledge message;
step S213, the layer 3 attachment is completed;
step S214, a PMIPv6 tunnel is established between the trusted non 3GPP access gateway and the P-GW, and the UE can send or receive data; the UE can access the dedicated services through the established PDN connection, and the PCRF also can make the corresponding policies for resource reservation according to the characteristics of the accessed services; these policies can be considered as the dedicated policies for accessing the services;
step S215, the UE decides to initiate to establish a second PDN connection to the APN, and the UE sends a request message of triggering new PDN connection establishment to the trusted non 3GPP access gateway, wherein the PDN identifier APN is carried in that message;
step S216, the trusted non 3GPP access gateway allocates the PDN Connection Id2 for uniquely differentiating the second PDN connection to be established;
the BBERF residing in the trusted non 3GPP access gateway sends the indication message of gateway control session establishment to the PCRF, and the user identifier NAI, the PDN identifier APN and the PDN Connection Id2 are carried in that message; that message makes a request for establishing one gateway control session (Gxx session), which is identified as the Gxx session2.
Step S217, the PCRF makes the PCC rule and the QoS rule according to the user subscription information, the network policy, the access network bearer attribute and so on, and at the same time, the PCRF may also make the corresponding event trigger; the PCRF sends the QoS rule and the event trigger to the trusted non 3GPP access gateway through the gateway control session establishment acknowledge message; and the trusted non 3GPP access gateway installs the QoS rule and the event trigger; these rules are not policies regarding to the specific services, but are some default policies;
step S218, the trusted non 3GPP access gateway sends the proxy binding update message to the selected P-GW, and the user identifier NAI, the PDN identifier APN and the PDN Connection Id2 are carried in that message;
step S219, the P-GW allocates the IP address, which is identified as IP Address2, of the established second PDN connection for the UE;
the PCEF residing in the P-GW sends the indication message of IP-CAN session establishment to the PCRF, and the user identifier NAI, the IP Address2, the PDN identifier APN and the PDN Connection Id2 are carried in that message; that message makes a request for establishing one Gx session, which is identified as the Gx session2.
Step S220, the PCRF associates the indication message of IP-CAN session establishment with the indication message of gateway control session establishment of step S216 according to the user identifier NAI, the PDN identifier APN and the PDN Connection Id2 after receiving the indication of IP-CAN session establishment, that is, associates the gateway control session (Gxx session2) established in step S216 with the IP-CAN session (Gx session2) established in step S219; at the same time, the PCRF inquires the user subscription information, updates the previously (step S217) made rules (including the PCC rule, QoS rule and event trigger) according to the user subscription information, the network policy, the bearer attribute of the access network and so on, and the PCRF sends the IP-CAN session establishment acknowledge message to the PCEF in the P-GW, wherein the PCC rule is carried in that message; these rules are not the policies regarding to the specific services, but are some default policies;
step S221, the PCEF in the P-GW installs and enforces the PCC rule carried in the IP-CAN session establishment acknowledge message after receiving the IP-CAN session establishment acknowledge message, and at the same time, the P-GW sends its own IP address to the HSS;
step S222, the P-GW returns the proxy binding acknowledge message to the trusted non 3GPP access gateway, and the proxy binding acknowledge message carries the IP address (IP Address2) allocated by the P-GW for the second PDN connection established by the UE;
step S223, if the QoS rule made in step S220 is different from that sent down in step S217, then the PCRF sends the updated QoS rule down to the trusted non 3GPP access gateway through the gateway control and QoS policy rule provision message;
step S224, the trusted non 3GPP access gateway installs the QoS rule, and returns the gateway control and QoS policy rule provision acknowledge message;
step S225, the trusted non 3GPP access gateway returns a reply message carrying the IP Address2 to the UE;
step S226, a second PMIPv6 tunnel is established between the trusted non 3GPP access gateway and the P-GW, and the UE can send or receive data; the UE will use the second established PDN connection to access some dedicated services in subsequent flows, and the PCRF will make the corresponding policies for the resource reservation according to the characteristics of the services, and these policies can be considered as the dedicated policies for accessing the services.
It can be seen from the above flow that, in order to support to establish multiple PDN connections to the single APN, the trusted non 3GPP access gateway should allocate one PDN Connection Id for each PDN connection with the same APN for uniquely differentiating each PDN connection accessing the same PDN. The PCRF associates the gateway control session (Gxx session) with the IP-CAN session (Gx session) according to the user identifier NAI, the PDN identifier APN and the PDN Connection Id.
The similar PDN establishment flow can also be used for accessing by the UE through the E-UTRAN, and the PMIPv6 protocol is adopted between the S-GW and the P-GW. The difference is that the PDN Connection Id is a bearer identifier of a default bearer of the PDN connection allocated by the MME when the access is based on the E-UTRAN.
FIG. 3 is a flow chart of a handover across the systems (namely, the handover from one non 3GPP system to another non 3GPP system) occurring after the UE establishes two PDN connections to the default APN according to the flow of FIG. 2 in the non roaming scenario according to the related art; and before the flow shown in FIG. 3 starts, it is assumed that the UE accesses through the trusted non 3GPP access network1 and establishes two PDN connections to the APN, and the UE accesses its own dedicated services through the two PDN connections respectively; the PCRF respectively makes the dedicated PCC rule and QoS rule for own dedicated services for the resource reservation of the bearer layer; the specific steps of the flow shown in FIG. 3 are as follows:
step S301, the UE detects a trusted non 3GPP access network2, and decides to initiate the handover;
step S302, the UE makes a request for performing the EPS access authentication to the HSS/AAA through the trusted non 3GPP access network after accessing the trusted non 3GPP access network2; the HSS/AAA authenticates the UE which sends the request after receiving the EPS access authentication request; and the HSS/AAA sends the IP address of the P-GW selected by the UE when accessing through the trusted non 3GPP access network1 and the user subscribed APN, including the default APN, to the trusted non 3GPP access gateway2 after completing the authentication on the UE;
step S303, a layer 3 attachment flow is triggered after the authentication succeeding;
step S304, the trusted non 3GPP access gateway2 supports to establish multiple PDN connections to the single APN, and the trusted non 3GPP access gateway2 allocates a PDN Connection Id3 for uniquely differentiating the PDN connection to be re-established;
the BBERF residing in the trusted non 3GPP access gateway2 sends the indication message of gateway control session establishment to the PCRF, wherein the user identifier NAI, the PDN identifier APN, the PDN Connection Id3 and the bearer attribute of the new access network are carried in that message, and that message makes a request for establishing one gateway control session (Gxx session), which is identified as the Gxx session3.
The bearer attribute of the access network includes: the IP-CAN type and BBERF address; besides, the bearer attribute of the access network can also include the Radio Access Technology (RAT) type.
It should be noted that, since there is no information exchange between the trusted non 3GPP access gateway1 and the trusted non 3GPP access gateway2, the respective allocated PDN Connection Ids are different.
Step S305, the PCRF determines that the handover of the UE occurs according to the bearer attribute of the new access network, and finds the information before the user hands over according to the user identifier NAI and the PDN identifier APN; however, since the PDN Connection Id3 is a new identifier, the PCRF is unable to judge which PDN connection before the handover should be associated (that is, which IP-CAN session (Gx session) before the handover is associated), thus the PCRF is unable to send down the dedicated policy related to a certain dedicated service accessed by the UE before the handover, but is only able to make the default QoS rule and event trigger according to information such as the user subscription information, the network policy, the bearer attribute of the new access network and so on, and sends these default QoS rule and event trigger to the BBERF in the trusted non 3GPP access gateway2 through the gateway control session establishment acknowledge message; and the BBERF located in the trusted non 3GPP access gateway2 installs the QoS rule and the event trigger;
step S306, the trusted non 3GPP access gateway2 sends the proxy binding update message to the P-GW, wherein the user identifier NAI, the PDN identifier APN and the PDN Connection Id3 are carried in that message; and step S306 can perform sending just after receiving the message (layer 3 attachment triggering message) of step S303 instead of waiting for the acknowledge message of step S305;
step S307, the P-GW in which the PCEF resides selects one PDN connection from the PDN connections established by the source system (i.e., the trusted non 3GPP access system1) to perform the re-establishment after receiving the proxy binding update message; and it is assumed that the P-GW decides to firstly re-establish the first PDN connection established in the source system for the UE, then the PCEF sends an indication message of IP-CAN session modification (in which that message modifies the first IP-CAN session, i.e., the Gx session1, established by the source system) to the PCRF, that message carries the PDN Connection Id3, and that message can also carry the user identifier NAI, the PDN identifier APN and the IP Address1;
step S308, the PCRF, after receiving the indication of IP-CAN session modification, associates the gateway control session establishment message of step S304 with the indication message of IP-CAN session modification according to the user identifier NAI, the PDN identifier APN and the PDN Connection Id3, that is, associates the new gateway control session (Gxx session3) with the first IP-CAN session (Gx session1) established in the source system; the PCRF is likely to modify the PCC rule, QoS rule and event trigger (including the default rules and the dedicated rules) of the first PDN connection established before the UE hands over according to the information such as the bearer attribute of the new access network and so on, and send the updated PCC rule and event trigger to the PCEF in the P-GW through an IP-CAN session modification acknowledge message; and the PCEF installs and enforces the PCC rule and the event trigger after receiving the IP-CAN session modification acknowledge message;
step S309, the P-GW returns the proxy binding acknowledge message to the trusted non 3GPP access gateway2, and the IP Address1 is carried in that message;
step S310, the PCRF sends the QoS rule and event trigger updated in step S308 down to the BBERF of the trusted non 3GPP access gateway2 through the gateway control and QoS policy rule provision message;
step S311, the BBERF located in the trusted non 3GPP access gateway2 installs the QoS rule and the event trigger, and returns the gateway control and QoS policy rule provision acknowledge message;
step S312, the layer 3 attachment is completed;
step S313, the PMIPv6 tunnel is established between the trusted non 3GPP access gateway2 and the P-GW, and the UE re-establishes the first PDN connection from the source system to the default APN; and the UE can access the dedicated services which have been applied for being accessed in the source system through that PDN connection;
step S314, the UE sends a triggering indication message to the trusted non 3GPP access gateway2, wherein, the APN and a handover indication are carried in that message, and the handover indication is used for indicating to re-establish one PDN connection before the handover to the trusted non 3GPP access gateway2;
step S315, the trusted non 3GPP access gateway2 in which the BBERF resides allocates a PDN Connection Id4 for uniquely differentiating the PDN connection to be re-established; the BBERF sends the indication message of gateway control session establishment to the PCRF, wherein, the user identifier NAI, the PDN identifier APN and the PDN Connection Id4 are carried in that message; that message makes a request for establishing one gateway control session (the Gxx session), which is identified as the Gxx session4;
step S316, the PCRF finds the information before the user hands over according to the user identifier NAI and the PDN identifier APN; however, since the PDN Connection Id4 is a new identifier, the PCRF is unable to bind the PDN Connection Id4 on a certain PDN connection before the handover, thus the PCRF is unable to send down the dedicated policy related to the dedicated service accessed by the UE before the handover; but is only able to make the QoS rule and the event trigger according to the user subscription information, the network policy and the bearer attribute of the current access network, and send these default QoS rule and event trigger to the BBERF in the trusted non 3GPP access gateway2 through the gateway control session establishment acknowledge message; and the BBERF of the trusted non 3GPP access gateway2 installs the QoS rule and the event trigger;
step S317, the trusted non 3GPP access gateway2 sends the proxy binding update message to the P-GW, wherein the user identifier NAI, the PDN identifier APN and the PDN Connection Id4 are carried in that message; and step S317 can perform sending just after receiving the message of step S314 instead of waiting for the acknowledge message of step S316;
step S318, the P-GW in which the PCEF resides, after receiving the proxy binding update message, selects one PDN from the PDN connections established by the source system to perform the re-establishment, and since only the second PDN connection established by the source system is left, the P-GW decides to re-establish the second PDN connection established in the source system for the UE; the PCEF sends the indication message of IP-CAN session modification (in which that message modifies the second IP-CAN session established by the source system, i.e., the Gx session2) to the PCRF, that message carries the PDN Connection Id4, and that message can further carry the user identifier NAI, the PDN identifier APN and the IP Address2;
step S319, the PCRF, after receiving the indication message of IP-CAN session modification, associates the gateway control session establishment message of step S315 with the indication message of IP-CAN session modification according to the user identifier NAI, the PDN identifier APN and the PDN Connection Id4, that is, associates the new gateway control session (Gxx session4) with the second IP-CAN session (Gx session2) established in the source system; the PCRF is likely to modify the PCC rule, QoS rule and event trigger (including the default rules and the dedicated rules) of the second PDN connection established before the UE hands over according to information such as the bearer attribute of the new access network and so on, and send the updated PCC rule and event trigger to the PCEF in the P-GW through the IP-CAN session modification acknowledge message; and the PCEF in the P-GW installs and enforces the PCC rule and the event trigger after receiving the IP-CAN session modification acknowledge message;
step S320, the P-GW returns the proxy binding acknowledge message to the trusted non 3GPP access gateway2, and the IP Address2 is carried in that message;
step S321, the trusted non 3GPP access gateway2 returns the reply message to the UE, wherein the IP Address2 is carried in that reply message;
step S322, the PCRF sends the QoS rule and event trigger updated in step S319 down to the BBERF in the trusted non 3GPP access gateway2 through the gateway control and QoS policy rule provision message;
step S323, the BBERF located in the trusted non 3GPP access gateway2 returns the gateway control and QoS rule provision acknowledge message;
step S324, another PMIPv6 tunnel is also established between the trusted non 3GPP access gateway2 and the P-GW, and the UE re-establishes the second PDN connection from the source system to the default APN; and the UE can access the dedicated services which have been applied for being assessed in the source system through that PDN connection.
It can be seen from the above flow that, when the handover of the UE across the systems occurs, since two access gateways are unable to interact, the PDN Connection Ids allocated respectively for supporting establishing multiple PDN connections to one APN are different. Therefore, when the PCRF receives the indication message of gateway control session establishment sent by the destination BBERF, the PCRF is unable to immediately associate it with a certain PDN connection (the IP-CAN session, i.e., the Gx session) established in the source system, but the PCRF has to wait for the P-GW making the selection, and makes the association according to the PDN Connection Id carried in the indication message of IP-CAN session modification.
However, in the prior art, it only discusses the method for performing the policy and charging control for establishing multiple PDN connections to one APN in the non roaming scenario. For the roaming scenario, the related art has not related to.
The EPS has two roaming architectures, the first one is home routed and the second one is local breakout. FIG. 4 is a roaming architecture diagram of the EPS of the home routed according to the related art, and as shown in FIG. 4, the P-GW is in the home network and the IP services are provided by the home network operator (namely, the AF is in the home network); FIG. 5 is a roaming architecture diagram of the EPS of the local breakout according to the related art, and as shown in FIG. 5, the P-GW is in the visited network and the IP services are provided by the home network operator (namely, the AF is in the home network), or the visited network operator provides the IP services (namely, the AF is in the visited network). For different roaming scenarios, the flows of the PCC are different, and the functions enforced by the PCC network element are also different.
At present, in the scheme of implementing the S9 roaming interface, the Visited PCRF (vPCRF) terminates the Gx sessions, existing in the visited network, of all the IP-CAN sessions established by the UE and the gateway control sessions (Gxx sessions), that is, the Gxx sessions and the Gx sessions will not be sent to the Home PCRF (hPCRF), but one S9 session is established between the vPCRF and the hPCRF, and that S9 session is used to transmit the information on the Gx sessions of all the IP-CAN sessions and the gateway control sessions (Gxx sessions), however, the Rx sessions, in the visited network, of all the IP-CAN sessions will not be terminated, the messages of the Rx sessions are only forwarded to the home PCRF, and the vPCRF is taken as one Proxy. Multiple subsessions (which are called as S9 subsessions) possibly exists in one S9 session, and each subsession is used for transmitting information on the Gx session of one IP-CAN session and the gateway control session (Gxx session).
In summary, the difficulty exists in performing the policy and charging control on multiple PDN connections established to one APN in the roaming scenario due to the complexity of the EPS roaming scenario and the complexity of the policy and charging control itself in the roaming scenario, and the related art has no corresponding solution yet.